The present invention is directed to the removal of unwanted compounds from liquids, and in particular to a recirculative treatment process and apparatus for removing undesirable components from wine.
It is a persistent problem in the production of wine that certain compounds are generated in intolerable concentrations, among which are ethyl acetate, acetic acid and acetaldehyde. These compounds appear naturally in wine, but are regarded as spoilage components because they so alter the flavor and aroma of the wine. Other components that may be considered undesirable include H.sub.2 S, ethyl mercaptan, dimethyl sulfide, and CO.sub.2.
It is possible to remove certain undesirable components in juices by reverse osmosis treatment, but this also removes important flavor and aroma components, resulting in a change in the nature of the wine in addition to volume loss and concentration effects. For instance, in U.S. Pat. No. 4,401,678 to Beaumont, a process for removing methyl anthranilate (which occurs in high concentration in Virus labrusca grapes) from grape juice by means of reverse osmosis treatment is discussed. The portion of the juice which passes through the reverse osmosis membrane, containing methyl anthranilate and other volatile esters as well as sugars and acids, is discarded, and the retentate is diluted with water to compensate for the higher concentration due to the reverse osmosis treatment. While this process does remove at least some of the undesirable components, it also removes many desirable components, so that the resulting juice is not suitable for making standard wines from Vitus vinifera grapes, i.e. classic wine grapes. In certain areas, such as California, the addition of water also renders the juice illegal for the production of standard wine.
There are other processes presently used for removing organic components from a fluid. For instance, in U.S. Pat. No. 4,643,902 to Lawhon et al. (particularly applicable to orange and grapefruit juice), ultrafiltration is used to isolate spoilage enzymes in a retentate, with the remainder of the juice in a permeate. The enzymes are deactivated, and the permeate and retentate may then be recombined. The permeate may be subjected to a reverse osmosis (R.O.) treatment-to concentrate the juice before recombination with the ultrafiltration retentate. After R.O. treatment and before recombination, the juice (i.e. R.O. retentate) may further be treated to deacidify it, such as by the use of an ion-exchange column. This produces a concentrate which is eventually rediluted (perhaps with the R.O. permeate, consisting of water) to reconstitute the juice.
This process would be deleterious in the production of high quality wine or any juice where the impact on the flavors and aromas is to be minimized, because anion exchange of the retentate removes both the undesirable components and components which are essential to the quality and value of the product.
Another approach to the removal of undesirable components from a fluid is discussed in the U.S. Pat. No. 4,808,287 to Hark, which uses R.O. treatment to produce ultrapure water. However, this disclosure is directed to the opposite of a problem solved by the present invention; it has as goals removing the components in the retentate (which are impurities), and keeping the entirety of the permeate.
There is thus a need for a process which can both selectively remove the undesirable components from a wine or juice and at the same time avoid concentration effects and minimize (1) the removal of components which provide aesthetic appeal, and (2) reduction in volume of the final product.